Particulate detergent compositions with improved environmental profiles could, in theory, be designed by eliminating all components from the composition that provide limited, or no, cleaning action. Such compact products would also reduce packaging requirements. However, to achieve this objective is difficult in practice because the manufacture of particulate detergent compositions usually requires the use of components that do not contribute significantly to detergency, but are nevertheless included to structure liquid ingredients into solids, to assist with processing and to improve the handling and stability of the particulate detergent compositions.
In our pending applications, PCT/EP2010/055256 and PCT/EP2010/055257 we propose to solve these problems by manufacturing a new particulate detergent composition. In general, the manufacture is done using a process comprising the steps of drying a surfactant blend, extruding it and cutting the extrudates to form hard core particles with a diameter of greater than 2 mm and a thickness greater than 0.2 mm. These large core particles are then preferably coated, especially with an inorganic coating.
Compositions comprising at least 70 wt % of these coated large particles with extruded surfactant cores differ from prior art extruded detergent compositions in that they have little or no solid structuring material to harden or structure the surfactant core. Instead, they use blends of low moisture surfactants to give hardness. The choice of surfactant allows the particles to give good detergency even without any conventional detergent builder, thus eliminating the need for such builders in the particles. Although the extruded particles are hard enough to cut to the required shape without deformation, they are hygroscopic and would stick together if not coated. It is therefore advantageous to coat the core particles by spraying inorganic material, such as sodium carbonate, onto them, in a fluid bed. The combination of the coating and the large particle size (5 mm diameter) substantially eliminates any tendency to deform or cake and allows production of a novel free-flowing composition of larger than usual detergent particles with excellent smooth and uniform appearance. Surprisingly, despite their large volume and high density, the particles are fast dissolving with low residues and form clear wash liquors with excellent primary detergency.
In PCT/EP2010/055257 a coating of inorganic salt (sodium carbonate) is applied to a large detergent core by spraying on a solution of the sodium carbonate in a fluidised bed of the cores. Because sodium carbonate is not highly soluble the process requires a large volume of water to be driven off to create a 20 to 30 wt % coating on the water soluble detergent core. Care has to be taken not to dissolve the core. The sodium carbonate coating process described is thus both time consuming and energy intensive.
Although we have produced very successful coatings from solutions of sodium carbonate they can be slow to produce, due to the limits on carbonate solution strength and the consequent high volume of water that must be removed to obtain a significant level (e.g. >20 wt %) of coating on the detergent particles. Furthermore, the fluidisation process has to be very closely and carefully controlled to avoid quenching of the bed.
U.S. Pat. No. 6,596,683B (P&G) also describes a process in which an inorganic aqueous solution is used to spray coat a core particle comprising detergent. The core also comprises inorganic builder material. Perhaps because of this the examples attain coating levels of only 2 wt % from the solutions of sodium carbonate. This is consistent with the teaching in column 10 that the inorganic solution is applied at a maximum level of 6%. Due to the presence of builder in the core there is no motivation to increase the coating level above the 6% maximum.
US2004235704A (P&G) describes the coating of detergent granules in a fluidised bed. The fluidised bed may be operated at a flux number of at least 3.5. Upon drying, the resultant detergent particles are said to have improved appearance and flow properties. Preferred coatings are non-hydrating inorganic salts, particularly Burkeite. As with most prior art the base particle that is being coated is taught, in paragraph 68, to include builder. The example used a 25% solution of Burkeite to give a 4% coating.
U.S. Pat. No. 6,858,572B (P&G) discloses a process for preparing detergent particles comprising a particle core of a detergent active material. This particle core is then at least partially covered by a particle coating layer of a water-soluble inorganic material. Particularly preferred are non-hydratable inorganic coating materials including double salt combinations of alkali metal carbonates and sulphates (Burkeite). The process includes the steps of passing the particle core through a coating mixer such as a low speed mixer or fluid bed mixer and coating the particle core with a coating solution or slurry of the water-soluble inorganic material. In a preferred embodiment the coating mixer is a fluidized bed. To achieve best results the nozzle location is placed at or above the fluidised height of the particles in the fluidised bed. The objective appears to be to create particles that are the same size and as spherical as possible. The coating zone of the fluidized bed is followed by a drying zone and then a cooling zone. Example 1 sprays on a 28.5 wt % Burkeite, or equivalent, solution to form a 5% coating. Example 2 sprays on a 67% potassium citrate solution to make a 5% coating. The higher solution concentration in example 2 means that less water has to be evaporated than in example 1. However, the coated particles would be sticky unless an additional dry coating is added on top. There is no enabling disclosure for spraying a slurry.
U.S. Pat. No. 3,989,635A (Lion) discloses a process for improving granular detergents. In Example 9 particles are coated with a 15% solution of sodium carbonate added to a fluidised bed together with sodium carbonate powder. The resulting 1 wt % coating is half from the solution and half from the separately added solids. The disadvantage of separate solids addition is that they adversely affect the appearance of the coating and they do not have the expected benefit of reducing the drying time compared to adding the entire solids loading in solution as done in other prior art.
US2004198629A (Henkel) discloses a detergent particle encapsulated with an insoluble material. The encapsulation layer is formed of polyvalent metal salts of hydroxylated fatty acid having at least 12 carbon atoms (e.g. zinc rincinoleate). The encapsulation material is preferably applied in the form of an aqueous dispersion in a fluidized bed. An exemplified coating suspension consisted of 16 wt % titanium dioxide, 16 wt % PEG 12000, 1.5 wt % of a mixture of 50 parts by weight of zinc ricinoleate, 35 wt % of triple-ethoxylated lauryl alcohol and 15 wt % tetra (2-hydroxypropyl)ethylenediamine (Tegosorb conc 50), 0.5 wt % sodium carboxymethylcellulose and the remainder water. Although SCMC is thus present in example 1 it is absent from the similar suspension in example 2 and thus cannot be considered as an essential part of the suspending system. This is consistent with the understanding of the skilled worker that a suspending polymer is not normally needed when there are large amounts of surfactant in a slurry. Thus the skilled person would understand that the SCMC is probably added to suspend the titanium dioxide pigment. It is not essential (as is clear from example 2) because the nonionic surfactant does the same job. The same skilled worker would normally turn to a polymer such as acrylic maleic copolymer even if surfactant were present.